UNIVERSITY   OF   CALIFORNIA 

COLLEGE    OF    AGRICULTURE 

AGRICULTURAL   EXPERIMENT   STATION 

BERKELEY,    CALIFORNIA 


PARADICHLOROBENZENE  AS  A 
SOIL  FUMIGANT 


E.  O.  ESSIG 


BULLETIN  411 

October,  1926 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1926 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/paradichlorobenz411essi 


PARADICHLOROBENZENE  AS  A  SOIL  FUMIGANT 

E.  O.  ESSIGi 


INTRODUCTION 

Paradichlorobenzene  was  first  demonstrated  as  a  commercial 
insecticide  in  1915  by  A.  B.  Duckett,2  Scientific  Assistant  in  the 
Bureau  of  Entomology  of  the  United  States  Department  of  Agricul- 
ture, who  showed  that  it  was  an  excellent  fumigant  for  stored-product 
insects,  case-bearing  clothes  moths,  roaches,  ants,  museum  pests,  and 
miscellaneous  household  insects. 

In  1919,  E.  B.  Blakeslee,3  also  of  the  Bureau  of  Entomology, 
issued  a  bulletin  on  the  control  of  the  peach  tree  borer  by  the  use  of 
toxic  gases  and  thus  paved  the  way  for  a  wide  field  of  experimental 
work  throughout  the  United  States  and  the  world.  A  number  of 
important  bulletins  from  various  experiment  stations  followed.4 
Practically  all  the  work  done  in  the  East  and  South  has  been  on  the 
peach  tree  borer,  Aegeria  exitiosa  Say,  an  insect  which  is  a  pest  chiefly 
on  peach  trees  grafted  on  peach  roots  in  those  sections.  In  the  experi- 
ments thus  conducted  excellent  results  have  been  obtained  in  the 
control  of  the  peach  tree  borer,  the  average  being  about  94  per  cent, 
but  all  eastern  and  southern  writers  caution  against  the  use  of  this 
soil  fumigant  on  peach  trees  less  than  three  years  old  and  on  apple 
and  pear  trees  of  any  age. 

Experiments  were  started  with  paradichlorobenzene  for  the  con- 
trol of  the  Pacific  or  California  peach  tree  borer,  Aegeria  opaleseens 
Hy.  Edw.,  in  the  summer  and  fall  of  1921  and  have  been  continued 
to  the  present  time.    Conditions  in  California  are  very  different  from 


1  Associate  Professor  of  Entomology  and  Associate  Entomologist  in  Experi- 
ment Station. 

2  Duckett,  A.  B.  Para-dichlorobenzene  as  an  insect  fumigant.  U.  S.  Dept. 
Agr.  Bur.  Ent.  Bui.  167:1-7,  pi.  2.     1915. 

s  Blakeslee,  E.  B.  Use  of  toxic  gases  as  a  possible  means  of  control  of  the 
peach-tree  borer.     U.S.  Dept.  Agr.  Bur.  Ent.  Bui.  796:1-23,  pi.  2.     1919. 

4  Peterson,  Alvah.  Some  soil  fumigation  experiments  with  para-dichloro- 
benzene for  the  control  of  the  peach  tree  borer,  Sanninoidea  exitiosa  Say.  Soil 
Science  11:305-318,  pi.  1.     1921. 

Paradichlorobenzene  (p-c-benzene)  for  controlling  the  peach-tree  borer. 
New  Jersey  Agr.  Exp.  Sta.  Circ.  126:1-12,  pi.  2.  1921;  Circ.  156  (revision  of 
above)  1923. 

Snapp,  O.  I.,  and  Alden,  C.  H.  Further  studies  with  paradichlorobenzene  for 
peach  borer  control.     U.S.  Dept.  Agr  Bui.  1169:1-18,  pi.  3.     1923. 

Guyton,  T.  L.,  and  Stear,  J.  R.  PDB  (paradichlorobenzene)  and  other  con- 
trols for  the  peach  tree  borer.    Pennsylvania  Dept.  Agr.  Gen.  Bui.  383:1-10.    1924. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

those  in  the  eastern  and  southern  states  and  the  results  obtained  have 
proved  to  be  of  interest  and  value.  Experiments  have  been  conducted 
not  only  for  the  control  of  the  Pacific  peach  tree  borer,  but  also  for 
woolly  apple  aphis,  Eriosoma  lanigera  (Hausmann)  ;  the  pear  root 
aphis,  Eriosoma  languinosa  Hartig ;  the  grape  phylloxera,  Phylloxera 
vitifoliae  Fitch;  wireworms;  and  the  garden  centipede,  Scutigerella 
immaculata  (Newport).  A  preliminary  report  was  made  in  19225  and 
a  short  review  appeared  in  1923  and  again  in  1925. 6  Since  the  pre- 
liminary investigations,  tests  and  demonstrations  have  been  conducted 
by  different  farm  advisors,  horticultural  commissioners,  and  farmers 
in  many  parts  of  California.  It  is  the  aim  of  this  bulletin  to  present 
the  data  available  from  all  these  sources  in  as  clear  and  brief  a 
manner  as  possible. 

The  wide  use  being  made  of  this  fumigant  is  well  illustrated  from 
the  fact  that  during  the  year  1924,  39,695  pounds,  and  in  1925, 
59,469  pounds,  or  a  total  of  99,164  pounds  for  the  two  years,  were 
used  in  California,  according  to  figures  furnished  by  one  of  the  lead- 
ing wholesale  distributors.  One  of  the  important  manufacturers 
estimates  the  amounts  used  in  California  as  about  50,000  pounds  in 
1924  and  120,000  pounds  in  1925.  These  figures,  while  not  accurate, 
serve  to  give  an  idea  of  the  large  amounts  of  this  material  now  being 
used  in  California.  The  counties  which  have  shown  the  greatest 
interest  in  paradichlorobenzene  used  approximately  the  following 
amounts  in  1924  and  1925:  Santa  Clara,  62,500  pounds;  Alameda, 
41,250  pounds;  San  Benito,  15,500  pounds;  Sonoma,  3250  pounds. 

The  reports  given  in  table  1  on  the  use  of  paradichlorobenzene  in 
various  parts  of  California  during  the  past  three  years  (1923,  1924, 
1925)  will  give  an  idea  of  the  extensive  trials  and  uses  of  the  material 
within  the  state. 


CHEMICAL    AND    PHYSICAL    PROPERTIES    OF 
PARADICHLOROBENZENE 

Paradichlorobenzene,  commonly  called  P  D  B,  is  a  white  crystalline 
material  and  appears  much  like  rock  salt  (fig.  1).  It  is  rather  volatile 
and  the  vapor  is  a  little  more  than  five  times  as  heavy  as  air  and 
slighly  more  than  twice  as  heavy  as  carbon  disulfid.  The  vapor  diffuses 
readily  through  the  air,  downward,  outward,  and  eventually  upward, 
and  has  a  strong  ether-like  odor  which  is  practically  non-poisonous 


s  Essig,  E.  O.  Para-Dichlorobenzene,  a  soil  fumigant.  Monthly  Bui.  Cali- 
fornia State  Dept.  Agr.  11:28-30.     1922. 

e  Home,  W.  T.,  Essig,  E.  O.,  and  Herms,  W.  B.  California  Agr.  Exp.  Sta. 
Circ.  265:80-81.     1923,  reprint  96-97.     1925. 


BUL.  411]  PARADICHLOROBENZENE    AS    A    SOIL    FUMIGANT 

TABLE   1 

General  Summary  of  Work  in  California  with  Paradichlorobenzene* 


County 

Person  conducting  or 
reporting  work  done 

Kinds  of 

trees 
treated 

Number 
of  trees 
treated 

Results 

Trees  killed 

Contra  Costa 

A.   M.   Burton,  Farm  Ad- 
visor. 

Pear 

50,000 

Good 

1 

Alameda 

J.  B.   Hammon,  Assistant 
Farm  Advisor. 

Apricot 

Prune 

Cherry 

330,000 

Excellent 

None 

Peach,  1  year 

200 

Only  2  borers 

None 

from  seed. 

found  when 
trees  dug. 

San  Benito 

W.   J.   Tocher,    Farm   Ad- 
visor. 

Apricot 
Prune 

15,500 

Good 

None 

Santa  Cruz 

Paul  Williamson,  Assistant 
Farm  Advisor. 

Apricot 
Apple 

7,500 

Good 

1 

Sonoma 

H.    P.    Everett,    Assistant 
Farm  Advisor. 

Apple 

25,900 

Good 

None 

Santa  Clara 

L.  R.  Cody,  Horticultural 
Commissioner. 

Apricot 
Prune 

550,000 

Good 

None 

Mendocino 

C.  S.   Myszka,  Farm  Ad- 
visor. 

Pear 

Poor 

18  trees  badly  in- 
jured or  killed! 

Napa 

H.  J.  Baade,  Farm  Advisor 

Apple 

4,000 

Good 

None 

Pear 

Lake 

L.  C.  Barnard,  Farm  Ad- 
visor. 

Pear 

2,000 

Good 

None 

*  A  number  of  other  counties  used  considerable  amounts  of  paradichlorobenzene  but  accurate  data 
could  not  be  obtained  as  to  the  work  done  and  results  secured. 

t  These  trees  were  given  an  extra  heavy  dose  and  the  surface  of  the  soil  was  wet  after  treatment. 
(See  full  statement,  p.  14). 


Fig.  1. — Crystals  of  paradichlorobenzene  and  two  types  of  measures.     The 
measures  hold  one  and  two  ounces  of  crystals  respectively. 


6  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

to  human  beings  but  is  very  toxic  to  insects,  affecting  chiefly  the 
nervous  system.  The  crystals  are  soluble  in  hot  alcohol  or  in  ether, 
benzene,  and  carbon  disulfid,  but  are  only  slightly  soluble  in  water. 
Volatilization  in  or  on  the  soil  is  very  slow  at  55°  F  and  more  rapid 
at  75°  F  or  above.  For  general  purposes  the  best  results  are  obtained 
when  the  soil  temperature  is  from  75°  to  85°  F.  In  the  soil  at  a 
temperature  of  75°  F,  from  three  to  six  weeks  are  required  for  com- 
plete volatilization,  while  at  low  temperatures  paradichlorobenzene 
may  remain  intact  throughout  the  winter  and  spring  under  most 
conditions. 

Because  of  its  volatility  paradichlorobenzene  is  packed  in  air-tight 
tin  or  other  containers  and  should  be  kept  sealed  in  such  when  not 
in  use. 

METHODS    OF    APPLICATION 

The  application  of  paradichlorobenzene  is  very  simple  and  is  based 
upon  the  fact  that  the  evolving  vapor  is  heavier  than  air  and  will 
gradually  settle  downward  if  protected  against  upward  and  outward 
diffusion.  It  is  placed  either  on  or  above  the  object  to  be  fumigated 
in  treating  grain,  carpets  and  clothing,  and  on  the  surface  of  the  soil 
or  in  a  trench,  for  the  control  of  soil  pests.  For  soil  treatments  the 
chemical  is  covered  with  a  layer  of  earth  to  prevent  an  upward  and 
outward  extension  of  the  vapor,  and  to  confine  it  so  that  it  will 
gradually  work  downward  to  the  haunts  of  the  pest. 

Various  recommendations  have  been  made  relative  to  the  time 
allowed  for  the  paradichlorobenzene  to  remain  about  the  tree  or  plant. 
Some  have  recommended  the  removal  of  the  residue  after  three  weeks 
from  the  date  of  application.  In  most  of  the  work  done  in  California, 
no  attempt  has  been  made  to  remove  the  residue  at  anytime  and  it 
does  not  appear  that  any  serious  injuries  have  resulted  from  this 
practice.  In  a  few  instances,  the  material  which  has  been  applied  in 
late  summer  or  fall  and  allowed  to  remain  throughout  the  winter  and 
spring,  gave  satisfactory  control,  whereas  material  applied  at  the  same 
time  but  removed  in  the  fall,  has  not  given  the  desired  results.  It  is 
recommended  that  the  paradichlorobenzene  be  left  until  entirely 
evaporated  or  until  farm  practices  require  its  removal,  excepting  in 
the  cases  of  nursery  stock  and  young  trees  as  herein  designated. 

Only  those  insects  which  live  at  or  below  the  surface  of  the  ground 
can  be  successfully  treated.  Flat  headed  borers  which  work  at  or 
below  the  surface  of  the  soil  may  be  controlled  but  those  working  on 
the  trunks  of  the  trees  above  the  ground  cannot  be  killed  by  this 
treatment. 


BUL.  411]  PARADICHLOROBENZENE    AS    A    SOIL    FUMIGANT 


Fig.   2 


Fig.  3 


Fig.  4 


Fig.  5 


Fig.  2. — The  ring  method,  first  step:  leveling  the  surface  of  the  ground  for 
a  space  of  two  or  three  feet  in  diameter  about  the  tree. 

Fig.  3. — The  ring  method,  second  step:  the  paradichlorobenzene  applied  in  a 
ring  two  or  three  inches  wide,  the  inside  about  three  inches-  from  the  bark  of 
the  tree. 

Fig.  4. — The  ring  method:  ring  of  paradichlorobenzene  applied  too  close  to 
the  tree.    Injuries  may  result  from  such  a  treatment. 

Fig.  5. — The  ring  method:  ring  of  paradichlorobenzene  applied  too  far  from 
the  bark  of  the  tree  for  the  control  of  the  Pacific  peach  tree  borer,  but  satis- 
factorily for  the  woolly  apple  aphis  and  pear  root  aphis. 


8.  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

APPLICATION  TO  TREES 

In  making  applications  to  trees  the  surface  of  the  soil  about  the 
trunk  is  first  smoothed  with  a  shovel  (fig.  2),  then  a  ring  of  para- 
dichlorobenzene  is  sprinkled  about  the  base  in  a  band  two  or  three 
inches  wide  and  with  the  inner  circumference  two  or  three  inches 
from  the  bark  of  the  tree  for  Pacific  peach  tree  borer  (fig.  3),  and 
from  four  to  six  inches  for  pear  root  aphis  or  woolly  apple  aphis 
(fig.  5).  The  ring  of  paradichlorobenzene  is  then  covered  with  a 
cone-like  mound  of  earth  (figs.  6  and  7).  The  whole  process  requires 
less  than  five  minutes  to  a  tree.  In  treating  the  woolly  apple  aphis 
on  large  trees  it  is  often  advisable  to  make  a  series  of  six  or  eight 
furrows  four  inches  deep  radiating  from  the  trunk  in  order  to  treat 
a  much  larger  root  area  (fig.  8).  The  material  is  sprinkled  in  the 
bottoms  of  the  furrows  and  then  covered  so  as  to  level  the  ground. 

USE  WITH  NURSERY  STOCK 

Nursery  stock  including  apples,  apricots,  cherries,  peaches,  pears, 
plums,  and  prunes  may  be  treated  by  means  of  a  single  furrow  two 
or  three  inches  from  the  row,  or  in  severe  infestations,  by  a  furrow 
on  each  side  of  the  row  from  four  to  six  inches  from  the  trees.  In 
the  eastern  and  southern  states  nursery  stock  and  young  trees  up  to 
six  years  of  age  are  often  severely  injured  by  this  treatment.  In 
California  our  experiments,  so  far,  have  shown  no  injury,  but  as  a 
precautionary  measure  it  is  recommended  that  the  treatment  of  all 
nursery  stock  and  young  trees  be  preceded  by  small  scale  tests  to 
ascertain  exact  effects  of  the  gas  in  every  locality  and  that  all  residue 
paradichlorobenzene  be  removed  three  weeks  after  treatment. 

DOSAGES 

One  of  the  most  difficult  problems  experienced  is  to  convince  the 
farmers  that  it  requires  but  a  very  small  amount  of  paradichloro- 
benzene to  control  most  soil  insects.  For  an  average  size  ten-year-old 
prune,  apricot,  or  apple  tree  from  iy2  to  2  ounces  is  all  that  should  be 
used  for  a  single  treatment.  In  severe  cases  as  much  as  3  or  4  ounces 
may  be  permissible,  but  more  than  that  amount  may  result  in  the 
permanent  injury  or  death  of  the  tree.  For  young  trees  less  than  six 
years  old,  %  ounce  is  sufficient.  For  the  nursery  trees  mentioned, 
1  ounce  distributed  along  one  yard  of  the  furrow  gave  satisfactory 
results  where  the  single  furrow  was  used.  Any  residue  of  para- 
dichlorobenzene remaining  after  three  weeks  should  be  removed. 


Bul.  411]  PARADICHLOROBENZENE    AS    A    SOIL    FUMIGANT  9 

It  is  very  difficult  to  lay  down  hard  and  fast  rules  for  dosages, 
because  of  the  great  variation  in  the  degree  and  extent  of  insect 
infestation,  especially  in  the  cases  of  the  woolly  apple  aphis  and  the 
pear  root  aphis  which  often  occur  on  the  roots  at  considerable  distances 
from  the  trunk. 


Fig.  6 


Fig.  8 


Fig.  7 


Fig.  9 


Fig.  6. — The  ring  method,  third  step:  covering  the  ring  of  paradichloro- 
benzene  with  earth. 

Fig.  7. — The  ring  method  completed  with  the  paradichlorobenzene  completely 
covered. 

Fig.  8. — The  radiating  furrow  method  of  treatment  for  woolly  apple  aphis, 
before  covering  the  furrows  with  earth. 

Fig.  9. — The  two-ring  method  of  treatment  for  woolly  apple  aphis. 


Excessive  doses  must  be  avoided  as  they  may  kill  the  trees  or  plants 
outright,  or  may  cause  a  lingering  death,  and  accomplish  no  more  in 
killing  the  pests,  than  the  amounts  recommended. 


10  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 


CONDITIONS   FOR  APPLICATION 

Two  conditions  of  the  soil  are  essential  to  successful  applications 
of  paradichlorobenzene  as  a  soil  fumigant.  They  are  proper  tempera- 
ture and  moisture.  As  previously  stated,  this  chemical  vaporizes  very 
slowly  at  55°  F,  and  is  more  effective  when  the  soil  temperature  is 
between  75°  and  85°  F. 

The  vapor  cannot  readily  penetrate  a  moisture-laden  soil ;  and,  on 
the  other  hand,  if  the  soil  is  too  dry  and  porous  the  gas  soon  dissipates. 
Therefore,  to  secure  best  results  one  must  select  a  time  when  the  soil 
is  neither  soaked  nor  entirely  dry.  It  is  not  necessary  to  allow  the 
trees  actually  to  suffer  for  want  of  water  in  order  to  make  successful 
treatments  with  the  chemical,  but  it  is  ordinarily  advisable  to  make 
the  applications  two  or  three  weeks  prior  to  irrigating  rather  than 
just  after.  Treatments  made  from  one  to  three  weeks  after  irrigation 
have  all  been  successful.  In  non-irrigated  soils  treatments  have  all 
been  successful  except  in  very  porous,  peaty,  or  coarse  gravelly  types 
which  were  not  sufficiently  compact  to  retain  the  gas. 

It  is  practically  useless  to  treat  a  cold  wet  soil,  first  because  of  the 
very  slow  formation  of  vapor,  and  secondly  because  the  vapor  cannot 
diffuse  in  the  water-logged  soil. 


TIME    OF    APPLICATION 

The  conditions  of  application  which  require  a  warm,  somewhat 
dry  soil  determine  the  time  of  application,  which  in  California  covers 
a  very  extended  period  because  of  the  long  dry  summers  and  autumns. 
While  treatments  may  be  made  as  early  as  May,  June,  and  July,  they 
are  usually  most  effective  in  late  August  and  in  September  and 
October  before  the  winter  rains  commence.  Any  time  that  the  soil 
temperature  to  a  depth  of  eight  to  twelve  inches  is  over  75°  F,  treat- 
ments may  be  made  if  the  soil  is  not  actually  wet.  Paradichloro- 
benzene applied  in  late  November  and  December  and  followed  by  cold 
wet  weather  may  remain  almost  intact  until  the  following  spring  or 
summer  when  the  rising  temperature  causes  it  to  diffuse  and  become 
effective.  This  practice  of  late  applications,  however,  is  not  economical 
or  practical  because  of  the  necessity  of  plowing  or  cultivating  before 
the  paradichlorobenzene  has  had  proper  conditions  to  do  its  work 
effectively. 


BUL.  411]  PARADICHLOROBENZENE    AS    A    SOIL    FUMIGANT  11 


USE    IN    CONTROLLING    THE    PACIFIC    PEACH    TREE    BORER 

Inasmuch  as  a  great  deal  of  work  with  paradichlorobenzene  was 
done  for  the  control  of  the  peach  tree  borer,  Aegeria  exitiosa  Say,  in 
the  eastern  states  and  in  Georgia,  it  was  natural  that  attention  in 
California  should  first  be  given  to  testing  this  fumigant  against  the 
Pacific  peach  tree  borer,  Aegeria  opalescens  Hy.  Edwards,  a  pest  of 
considerable  proportions  in  some  parts  of  the  San  Francisco  Bay  region, 
particularly  in  San  Mateo,  Santa  Clara,  San  Benito,  and  Alameda 
counties.  Here  the  laborious  methods  of  worming  or  digging  out,  as 
well  as  the  less  satisfactory  asphaltum  treatment,  were  not  only 
difficult  and  expensive,  but  often  resulted  in  as  much  injury  to  the 
tree  as  that  done  by  the  borers.  Preliminary  tests  demonstrated  at 
once  the  efficacy  of  the  paradichlorobenzene  treatment  and  immedi- 
ately presented  an  unexplored  field  in  the  control  of  agricultural  pests, 
and  particularly  those  difficult  and  hitherto  almost  uncontrollable 
forms  which  inhabit  the  soil. 


KINDS    OF   TREES   TREATED 

In  California,  the  Pacific  peach  tree  borer  attacks  a  variety  of 
trees  on  different  rootstocks,  so  that  the  problem  here  was  much  more 
varied  than  in  the  East,  where  only  the  peach  on  its  own  roots  was 
treated.    Among  the  hosts  are  peaches,  cherries,  prunes,  and  apricots. 

Cherries.  Cherry  trees  are  only  occasionally  infested  by  the  peach 
tree  borer. 

Peaches.  The  acreage  of  peaches  grown  in  the  region  infested  by 
the  peach  tree  borer  is  small  as  compared  with  that  of  prunes  and 
apricots  and  the  number  of  trees  treated  was  relatively  small ;  however, 
a  large  amount  of  peach  nursery  stock  is  grown  therein  and  it  was 
often  seriously  infested.  A  number  of  experiments  in  treating  one- 
year-old  budded  and  grafted  trees  were  made  in  three  different 
nurseries  without  any  noticeable  injury.  The  material  was  applied 
in  a  small  furrow  from  two  to  four  inches  deep  and  from  two  to  three 
inches  from  the  young  trees  at  the  rate  of  2  ounces  to  a  yard.  The 
furrow  was  then  covered. 

Prunes.  Approximately  80,000  acres  of  French  prunes,  chiefly  on 
Myrobalan  and  peach  rootstocks,  were  treated.  The  ages  of  the  trees 
varied  from  four  to  twenty-five  years,  the  very  large  majority  being 
over  ten  years.     Control  of  the  borers  averaged  from  80  per  cent  to 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

95  per  cent  in  most  cases,  and  in  a  few  instances  approached  extermi- 
nation for  the  season.  During  the  past  four  years  thousands  of  acres 
have  been  treated  without  the  loss  of  a  single  tree  or  evident  injury 
to  any. 

Apricots.  Apricot  trees  make  up  the  largest  acreage  treated.  A 
few  orchards  are  on  apricot  roots  and  these  are  very  nearly  immune  to 
the  attacks  of  the  peach  tree  borer.  The  majority  of  the  older  apricot 
trees  are  on  Myrobalan  rootstocks  and  these  are  very  susceptible  to 
borer  attacks.  As  many  as  one  hundred  and  twenty  borers  have  been 
taken  by  the  old  worming  process  from  a  single  large  fifteen-year-old 
tree,  and  from  sixty  to  eighty  from  many  other  trees  of  the  same  age 
or  older.  All  ages  of  trees,  from  those  just  set  out  to  those  twenty-five 
or  thirty  years  old,  were  treated.  The  only  injury  noted  was  to  large 
roots  which  were  almost  exposed  at  the  surface ;  some  of  these  were 
either  injured  or  killed  by  the  gas  and  the  trees  themselves  greatly 
weakened. 

Practically  all  of  the  330,000  trees  treated  in  Alameda  County  in 
1924  were  apricot  trees  infested  with  the  Pacific  peach  tree  borer. 
During  the  past  three  years  no  serious  injury  to  any  of  these  trees  has 
been  noted.  Table  2,  giving  results  of  demonstrations  conducted  in 
Alameda  County  by  Assistant  Farm  Advisor  J.  B.  Hammon,  will  give 
a  fair  idea  of  results  obtained  there. 

The  dosage  of  parabichlorobenzene  for  control  of  the  Pacific  peach 
tree  borer  is  1  ounce  for  an  average  tree.  On  very  large  trees  it  may 
be  increased  to  1%  or  2  ounces.  Nursery  stock  treated  by  the  furrow 
system  should  receive  about  1  ounce  to  a  linear  yard  of  furrow. 

The  material  is  applied  in  a  concentric  ring  about  three  inches 
from  the  bark  of  the  tree  trunk.  (See  Methods  of  Application,  page 
6,  and  figs.  2-9.) 

Usually  but  one  application  a  year  is  necessary.  In  severely 
infested  districts  where  all  orchards  are  not  treated  or  where  a  com- 
plete clean-up  has  not  been  secured  from  a  single  treatment  it  is 
advisable  to  make  a  follow-up  treatment  the  succeeding  year. 

The  material  may  be  applied  with  fair  success  from  May  to 
November  but  best  results  have  been  secured  from  applications  made 
in  September  and  October.     (See  Time  of  Application,  page  10.) 


BUL.  411]  PARADICIILOROBENZENE    AS    A    SOIL    FUMIGANT 


13 


TABLE  2 

Report  on  Some  Trial  Plots  for  the  Use  of  Paradichlorobenzene  to  Control 

Pacific  Peach  Tree  Borer  on  Apricots,  Cherries,  Peaches, 

and  Prunes  in  Alameda  County 


Name 

Variety 
of  fruit 

Size* 
of 
plot 

Age  of 
trees, 

Years 

Spring 
treated 

Time 
dug 

Per 

cent 
con- 
trol 

Fall 
treated 

Time 

of 
exam- 
ination 

Per 

cent 
con- 
trol 

Condition 
of  trees 
6  months 

after 
treatment 

J.  J.  Silveria 

Silver 
prune 

10  A 

30 

Oct. 

3  wk. 
6  mo. 

30 

97 

Good 

Chas.  Long 

Apricot 

5A 

8 

Oct. 

6  mo. 

95 

Good 

F.  Cober 

Peach 

200  T 

Kin 
nursery) 

Sept. 

3  wk. 

99 

Good 

J.  A.  Borgas 

Apricot 

10  A 

28 

May 

3  wk. 

35 

Sept. 

8  wk. 

98 

Good 

J.  H.  Langdon 

Apricot 

10  T 

6 

Sept. 

6  mo. 

98 

Good 

Ed.  Chadburne... 

Apricot 

140  A 

35 

May 

6  wk. 

75 

Sept. 

Not  dug 

(100) 

Good 

H.  H.  Jameson 

Apricot 

10T 

12 

Oct. 

3  wk. 

10 

No  im- 
provement 

Driscol 

Apricot 

80  A 

12 

Oct. 

8  mo. 

97 

Good 

M.  V.  Perry 

Prune 

75  A 

12 

May 

6  wk. 

37 

Sept. 

Not  dug 

No 
report 

Good 

H.  L'Ecuyer 

Apricot 

10  A 

6 

June 

6  wk. 

50 

Oct. 

3  wk. 
6  mo. 

80 
96 

Good 

F.  A.  Stevens 

Cherry 

10  T 

15 

Sept. 

8wk. 

95 

Good 

P.  H.  Moore 

Apricot 

10  T 

35 

June 

6  wk. 

35 

No  im- 
provement 

A=Acres,  T  =  Trees. 


FOR   USE   IN   CONTROLLING  THE   PEAR   ROOT  APHIS 

Two  years  of  experimental  and  demonstrational  work  with  para- 
dichlorobenzene on  the  pear  root  aphis,  Eriosoma  languinosa  Hartig, 
were  conducted  in  Contra  Costa  County  in  cooperation  with  Mr.  A. 
M.  Burton,  Farm  Advisor.  These  experiments  proved  the  treatment 
to  be  efficacious  on  all  ages  of  pear  trees  grafted  to  both  French  and 
Japanese  rootstocks.  According  to  Mr.  Burton,  237  acres  of  pear 
trees  were  treated  in  1924,  and  more  than  230  acres  in  1925,  in  Contra 
Costa  County.  During  the  two  years  only  one  tree  was  killed  and 
there  was  no  appreciable  injury  to  others. 


14  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

In  Mendocino  County,  Farm  Advisor  C.  S.  Myszka  conducted  an 
experiment  in  which  doses  of  2,  4,  and  8  ounces  of  paradichloro- 
benzene  were  used  on  four-year-old  trees.  The  material  was  applied 
around  the  trees  in  circular  trenches  of  two-foot  radius.  Water  was 
afterwards  applied  to  wet  the  surface  of  the  soil  around  eighteen 
of  the  trees  which  had  received  the  heavier  dosages  with  the  result  that 
these  trees  were  either  badly  damaged  or  killed.  This  can  likely  be 
explained  by  the  combination  of  the  extra  heavy  dosages  and  the  wet 
surface  soil  which  confined  the  evolving  gas  about  the  roots  of  the 
tree.  No  injury  was  noted  even  with  the  heavier  dosages  where  water 
was  not  thus  applied. 

Irrigation  immediately  after  the  application  of  paradichloro- 
benzene  has  not  injured  any  of  the  thousands  of  trees  treated.  This 
is  undoubtedly  due  to  the  fact  that  the  soil  when  thoroughly  wet  does 
not  permit  of  a  ready  penetration  of  the  gas  while  the  lower  tempera- 
ture delays  its  rapid  evolution  and  beneficial  results  in  insect  control 
will  not  follow  until  the  soil  becomes  warm  and  dry  enough  to  permit 
of  the  proper  evolution  and  penetration  of  the  gas. 

Other  orchard  treatments  have  been  made  in  Lake  and  Sonoma 
counties  with  very  satisfactory  results. 

The  proper  dosage  of  paradichlorobenzene  for  the  control  of  pear 
root  aphis  is  from  1  to  1%  ounces  to  a  tree. 

The  material  is  applied  in  a  concentric  ring  four  to  six  inches 
from  the  tree.     (See  Methods  of  Application,  page  6,  and  figs.  2-9.) 

Usually  but  one  application  is  necessary.  It  is  made  preferably 
in  early  summer,  in  June  or  July,  but  may  be  made  any  time  from 
June  until  November. 


USE   IN   CONTROLLING   THE  WOOLLY  APPLE   APHIS 

Experiments  and  demonstrations  with  paradichlorobenzene  for  the 
control  of  the  woolly  apple  aphis,  Eriosoma  lanigera  (Hausmann), 
were  conducted  in  Alameda,  Sonoma,  and  Santa  Cruz  counties.  In 
all,  several  thousand  trees  were  treated,  including  nursery  trees,  three- 
and  four-year-old  trees,  and  mature  trees  ten  years  of  age  and  over. 
In  Sonoma  County,  6400  apple  trees  were  treated  in  1924,  and  18,000 
in  1925. 

The  injury  reported  to  apple  trees  in  the  East  is  not  at  all  apparent 
from  the  work  done  to  date  in  California.  So  far,  the  only  injury 
noted  has  been  to  trees  having  one  or  more  of  the  main  roots  near  the 


BUL.  411]  PARADICHLOROBENZENE    AS    A    SOIL    FUMIGANT  15 

surface  of  the  soil.  Several  trees  have  been  greatly  weakened,  and  a 
few  have  actually  been  killed.  It  has  not  been  satisfactorily  estab- 
lished that  the  paradichlorobenzene  caused  the  death  of  these  few  trees. 

Very  satisfactory  results  have  been  obtained,  on  the  whole.  Infes- 
tations far  out  on  the  roots  are  difficult  to  kill,  but  are  much  less  serious 
than  those  near  the  crown.  Constant  reinfestation  from  the  tops  by 
flying  migrants  make  yearly  treatments  necessary.  Paradichloro- 
benzene treatment  should  be  combined  with  the  application  of  oil 
sprays,  the  former  made  in  late  summer  and  in  fall  and  the  latter 
during  the  dormant  winter  period,  to  reduce  the  infestations  of  the 
trunks  and  tops  of  the  trees. 

The  dosage  of  paradichlorobenzene  for  the  control  of  woolly  apple 
aphis  is  from  1  to  1%  ounces  to  a  tree.  In  Sonoma  County,  Assistant 
Farm  Advisor  H.  P.  Everett  recommends  as  a  normal  dose,  1  ounce 
to  a  tree  applied  in  a  single  ring  six  inches  from  the  tree,  but  in  severe 
infestations  1%  ounces  are  used  in  two  rings  (fig.  9).  Excessive 
doses  are  believed  by  some  growers  in  certain  localities  to  have  caused 
injury. 

The  material  is  applied  in  one  or  two  concentric  rings  or  in  radiat- 
ing furrows.     (See  Methods  of  Application,  page  6,  and  figs.  2-9.) 

From  one  to  three  applications  may  be  made,  depending  upon  the 
seriousness  of  the  infestation.  They  may  be  made  any  time  during 
the  summer  and  fall  when  the  soil  has  a  temperature  of  55°  F  or 
over.  Normally,  one  application  a  year  is  sufficient.  Because  of  the 
constant  migrations  of  the  winged  females  from  tree  to  tree,  it  is 
necessary  to  keep  constant  watch  of  the  orchards  and  repeat  the 
treatment  each  year  that  the  aphis  is  present. 


USE  IN  CONTROLLING  THE  RASPBERRY  CANE  BORER 

Mr.  H.  J.  Ryan,  County  Horticultural  Commissioner  of  Los 
Angeles  County,  conducted  some  extensive  tests  with  paradichloro- 
benzene in  the  control  of  the  raspberry  cane  borer,  Bembecia  mar- 
ginata  (Harris).  He  has  very  kindly  furnished  a  copy  of  the  report 
on  this  work,  from  which  the  following  information  was  secured. 

The  work  was  conducted  in  more  than  a  hundred  separate  patches 
of  raspberry  and  blackberry  plantings  on  light  and  heavy  soils  in  the 
San  Fernando  Valley.  All  treatments  were  made  between  June  7 
and  July  17.  The  method  of  treatment  is  similar  to  that  already 
described  on  pages  6  to  10,  and  consists  in  first  leveling  the  soil  about 


16  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

the  bases  of  the  infested  plants,  then  applying  the  material  in  a  circle 
or  ring  and  covering  it  with  three  or  four  inches  of  soil.  The  recom- 
mended dosage  is  %  ounce  for  the  smaller  plants  and  %  ounce  for 
the  larger  ones.  Based  on  twenty  cents  a  pound  for  the  paradichloro- 
benzene  and  1200  berry  plants  to  the  acre,  the  cost  is,  including  labor, 
from  forty-three  to  forty-five  dollars  an  acre. 

This  experience  in  California  is  contrary  to  that  of  New  Jersey, 
where  paradichlorobenzene  applied  at  the  rate  of  from  %  to  2  ounces 
to  a  blackberry  bush  and  left  for  three  weeks  "killed  most  of  the 
borers  and  injured  and  in  most  cases  killed  the  bushes."7 


USE    IN   CONTROLLNG   THE    GRAPE    PHYLLOXERA 

Experiments  with  paradichlorobenzene  for  the  control  of  grape 
phylloxera,  Phylloxera  vitifoliae  Fitch,  have  been  conducted  in  only 
two  counties  and  on  a  very  limited  scale.  Mr.  C.  S.  Myszka  conducted 
two  tests  in  Mendocino  County  on  grapevines  which  were  very 
seriously  infested  with  this  insect.  One  test  involving  one  hundred 
vines  was  made  in  June,  1922.  From  8  to  16  ounces  to  a  vine  was 
used,  applying  in  furrows  radiating  from  the  vines.  Some  of  the 
vines  showed  injury  soon  after  treatment.  Subsequent  examination 
of  the  roots  of  the  treated  vines  showed  no  evidences  of  phylloxera, 
while  roots  from  the  check  vines  showed  great  numbers  present.  The 
next  spring  insects  were  found  on  the  roots  of  the  treated  vines  in 
limited  numbers,  but  the  injured  vines  had  made  a  noticeable  advance 
in  growth  over  the  infested  and  untreated  vines  in  the  same  vineyard. 

Another  experiment  conducted  in  July,  1923,  involved  two  plots, 
one  on  gravelly  loam  soil  and  another  on  clay  loam  soil.  One-half 
ounce  of  paradichlorobenzene  to  a  vine  was  used,  applied  as  in  the 
first  test.  In  November  of  that  year,  examination  showed  practically 
no  control  on  the  light  soil,  while  no  insects  could  be  found  on  the 
vines  in  the  heavier  soil. 

The  experiment  on  the  gravelly  soil  bears  out  the  observation  that 
very  porous  soils  do  not  confine  the  gas  sufficiently  to  secure  control 
with  ordinary  doses. 

From  the  results  of  these  limited  preliminary  tests  it  will  be  seen 
that  as  yet  no  specific  recommendations  can  be  made  for  the  control 
of  phylloxera  on  grapevines. 


7  Peterson,   Alvah.      Paradichlorobenzene    (p-c-benzene)    for   controlling   the 
peach-tree  borer.     New  Jersey  Agr.  Exp.  Sta.  Circ.  156:12.     1923. 


BUL.  411]  PARADICHLOROBENZENE    AS    A    SOIL    FUMIGANT  17 


USE    IN    CONTROLLING    WIREWORMS    IN    DAHLIAS 

A  large  number  of  experiments  were  performed  during  the  spring 
of  1924  in  cooperation  with  F.  H.  Wymore8  to  determine  the  efficacy 
of  paradichlorobenzene  for  combating  wireworms  in  planted  dahlia 
tubers.  The  species  of  wireworms  was  not  determined.  These  experi- 
ments were  carried  out  in  sandy  soil  in  Alameda  in  a  patch  where  a 
great  number  of  tubers  were  already  so  badly  infested  that  the  owner 
was  ready  to  abandon  the  entire  lot  of  several  hundred  fine  varieties. 


Surface  oj_Sol2__^_^ 

ggJ^BBJjmparadichloro   benzene  fc,*^ 

■■"■;■•■■■ 

^r                    Dahlia  Root          ^A 

o> 


Fig.   10. — Method  of  treating  dahlia  with  paradichlorobenzene  to 
control  wireworms. 

Tubers  containing  from  twenty-five  to  fifty  worms  were  returned 
to  their  former  position  and  covered  with  about  two  inches  of  soil. 
Various  amounts  of  paradichlorobenzene  were  then  added  and  the  top 
soil  replaced.  These  infested  tubers  were  taken  up  and  examined  in 
seven  days  and  in  no  case  were  any  wireworms  located  in  the  tubers. 
A  few  dead  ones  could  be  found  in  the  soil,  but  the  great  majority 
could  not  be  accounted  for.  So  promising  were  these  preliminary 
results  that  practically  the  entire  patch  was  treated.  The  retarded 
plants  at  once  took  on  new  life  and  an  excellent  crop  of  flowers  and 
tubers  was  produced  in  the  face  of  what  seemed  sure  ruin.    The  dosage 


Research  Assistant  in  the  Division  of  Entomology  and  Parasitology. 


18  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

used  was  approximately  one  teaspoonful  placed  about  two  inches  above 
the  planted  tuber  as  illustrated  in  figure  10.  From  these  experiments 
we  concluded  that  the  chemical  acted  chiefly  as  a  repellent,  but  it  was 
so  effective  that  not  a  single  living  wireworm  was  to  be  found  in  any 
of  the  several  hundred  tubers  treated. 


USE   IN   CONTROLLING   THE   GARDEN    CENTIPEDE 

Mr.  Wymore  has  conducted  a  large  number  of  experiments  with 
paradichlorobenzene  in  the  control  of  the  garden  centipede,  Scuti- 
gerella  immaculata  (Newport),  on  asparagus  which  may  be  sum- 
marized as  follows : 

1.  The  tests  were  made  largely  on  loose  peaty  soils  of  the  delta 
asparagus  growing  section. 

2.  Preliminary  tests  in  which  one  ounce  of  paradichlorobenzene 
was  used  to  three  linear  feet  of  furrow  gave  good  results  in  killing  the 
centipede  when  applied  close  to  and  on  both  sides  of  the  row.  These 
tests  were  made  in  May  when  the  soil  was  noticeably  moist  and  its 
temperature  58°  F.9 

3.  Applications  of  large  amounts  of  paradichlorobenzene  were 
made  later  as  follows: 

(a)  On  August  9,  1923,  175  pounds  was  applied  at  the  rate  of 
1  ounce  to  every  three  linear  feet  in  the  row  between  the  asparagus 
rows,  with  a  beet  drill.  The  rows  of  paradichlorobenzene  were  twenty 
inches  apart  and  four  or  five  inches  deep. 

(6)  On  the  same  date  125  pounds  of  the  material  was  applied  in  a 
furrow  on  each  side  of  the  rows  of  asparagus  by  first  making  a  furrow 
with  a  small  hand  wheel  plow  and  applying  the  material  by  hand. 
The  amount  used  and  depth  applied  was  the  same  as  in  the  preceding 
test. 

(c)  In  July,  1924,  one-eighth  acre  of  asparagus  was  treated  at  the 
rate  of  460  pounds  to  an  acre.  The  material  was  applied  at  a  depth 
of  five  or  six  inches  in  six  or  seven  furrows  between  every  two  rows 
of  asparagus. 

4.  In  all  of  the  above  three  tests  ideal  moisture  and  temperature 
conditions  for  the  dissemination  of  the  gas  prevailed  in  the  soil  for 
at  least  a  week  after  the  work  was  finished. 


9  Wymore,  F.  H.  The  garden  centipede,  Scutigerella  immaculata  (Newport), 
a  pest  of  economic  importance  in  the  West.  Pomona  Col.  Jour.  Ent.  and  Zool. 
16:73-88,  fig.  5.     1924. 


BlTL.  411]  PARADICHLOROBENZENE    AS    A    SOIL    FUMIGANT  19 

5.  The  results  obtained  were  not  at  all  satisfactory  since  large 
numbers  of  live  centipedes  could  be  found  about  the  crowns  of  the 
asparagus  a  week  after  the  material  was  applied. 

6.  The  unsatisfactory  results  obtained  are  believed  to  be  due  to  the 
rapid  escape  of  the  vapor  because  of  the  very  porous  condition  of  the 
peaty  soils  where  the  tests  were  made. 


OTHER   USES 

Because  of  its  persistent  odor  and  deadly  effects  to  insects  gener- 
ally and  its  comparatively  harmless  effects  to  human  beings,  para- 
dichlorobenzene  may  also  be  used  for  many  other  purposes. 

1.  Fumigating  cereals  and  other  food  products  in  mills,  granaries, 
warehouses,  storerooms,  residences,  etc. 

2.  Fumigating  furs  and  textiles  in  stores  and  residences. 

3.  Fumigating  botanical  and  insect  museum  specimens. 

In  all  the  above  cases  the  material  is  placed  in  shallow  open  con- 
tainers under  as  warm,  dry  and  confining  conditions  as  possible  and 
the  vapor  allowed  to  evolve  as  rapidly  as  it  will.  For  clothing,  furs, 
and  museum  specimens  it  is  used  the  same  as  napthalene  or  moth  balls, 
but  is  much  more  effective  in  destroying  insects  pests  than  are  these 
agents. 

WARNING 

Although  paradichlorobenzene  has  been  extensively  used  over  a 
period  of  five  years  in  California  there  is  still  much  to  be  learned 
regarding  it  and  a  great  deal  of  experimental  work  remains  yet  to  be 
done.  The  action  of  the  vapor  on  the  roots  of  the  plants  is  so  slow 
that  the  after  effects  may  not  be  noticed  for  several  years,  and  trees 
treated  in  the  preliminary  tests  of  1921  are  still  under  observation. 
While  a  single  treatment  may  produce  no  ill  effects  we  are  not  now 
able  to  determine  what  results  may  develop  from  successive  treat- 
ments over  a  period  of  years.  Therefore,  the  growers  should  take 
all  precautionary  measures  possible  and  at  least  observe  the  following : 

1.  Avoid  using  excessive  dosages. 

2.  Do  not  place  the  crystals  in  contact  with  the  bark  of  the  trunks, 
stems,  or  the  roots  of  the  plants. 

3.  Do  not  apply  the  material  immediately  before  or  after  irri- 
gation and  do  not  wet  the  surface  of  the  soil  following  applications 
of  the  crystals. 


20  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

4.  In  treating  nursery  stock  and  young  trees  remove  the  residue 
after  three  weeks. 

5.  Do  not  apply  paradichlorobenzene  during  the  winter  and  early 
spring.    Late  summer  and  fall  are  the  best  times  for  such  applications. 

6.  Only  one  application  a  year  is  advisable.  Several  treatments  in 
one  season  may  be  fatal  to  the  plants. 

7.  Paradichlorobenzene  is  recommended  in  the  orchard  and  garden 
only  for  insects  which  attack  the  plants  at  or  below  the  surface  of 
the  soil  and  cannot  be  used  for  borers  which  infest  the  trunks  and 
limbs  above  the  ground. 


COSTS    OF    MATERIAL   AND    APPLICATIONS 

The  price  of  paradichlorobenzene  is  variable  but  ranges  around 
thirty -five  cents  a  pound  retail  in  small  lots,  and  twenty-five  cents  a 
pound  in  larger  lots  of  a  hundred  pounds  or  over.  The  total  cost  of 
chemicals  and  labor  for  treating  a  vine  or  a  tree  should  not  exceed 
five  cents  because  of  the  small  dosage  and  ease  of  application.  In 
most  cases  the  average  cost  in  orchards  was  four  cents  a  tree. 

Paradichlorobenzene  is  available  in  small  lots  through  many  local 
insecticide  dealers  and  florists  under  various  trade  names  such  as 
"Crystal  Glass,"  "Paracide,"  "P.B.D."  "Paradi,"  and  so  forth. 
For  all  practical  purposes  these  materials  appear  to  be  identical. 


lOm-10,'26 


